1. Field of the Invention
The present invention relates to a method of left ventricular volume evaluation, and more particularly, to a method of left ventricular volume evaluation in which nuclear magnetic resonance imaging is utilized.
2. Description of the Background Art
In the diagnosis of the heart, it is clinically important to know the left ventricular volume accurately, because of the importance of the function of the left ventricle in the heart. As examples of a conventional method for evaluating this left ventricular volume, several methods including an intracardiac catheterization method, a radiocardiography (cardiac radioactive isotope) method, and an echocardiography method are known.
In the intracardiac catherization method, a contrast medium is injected into the heart, and the contour of the left ventricle is X-ray imaged by utilizing the contrast produced by the irradiation of X-ray, such that the left ventricular volume can be evaluated on a basis of the X-ray imaged left ventricular contour. Now, in such an intracardiac catheterization, the X-ray image of the left ventricle is a projection from a point X-ray source, so that the X-ray imaged left ventricular contour is enlarged compared with the actual size, and there is a need to take the enlarging rate into account in order to evaluate the left ventricular volume accurately. However, the determination of this enlarging rate requires the accurate knowledge of the distances among the X-ray source, left ventricle, and X-ray film, so that the accurate determination of the enlarging rate has been impossible, and consequently the accurate evaluation of the left ventricular volume using the intracardiac catheterization has been impossible.
Moreover, in the intracardiac catheterization method, the injection of the contrast medium affects the state of the heart and causes a change of the size of the left ventricle from its normal size, so that the accurate evaluation of the left ventricular volume is actually impossible.
In the radiocardiography method, the radioactive isotope is used instead of the contrast medium in the intracardiac catheterization method, and the X-ray image of the left ventricular contour is obtained and utilized in a manner similar to the intracardiac catheterization method. In this radiocardiography method, the sensitivity of the radioactive isotope detector is rather low, so that the accurate imaging of the left ventricular contour is impossible, and consequently the accurate evaluation of the left ventricular volume using the radiocardiography has been impossible.
In the echocardiography method, the left ventricular contour is obtained by using the echos resulting from the irradiation of ultrasonic waves by an ultrasonography apparatus, and the left ventricular volume is evaluated on a basis of the obtained left ventricular contour. However, in such an echocardiography, the radiation angle for the ultrasonic waves emitted from the ultrasonic probe is small, i.e., a region of irradiation by the ultrasonic waves is small, so that there have been situations in which it is impossible to take an entire image of the heart, and consequently the accurate evaluation of the left ventricular volume using the echocardiography has been impossible.